Assembly of shielded connectors and a board having plated holes

ABSTRACT

Assembly provided with at least one shielded connector(2, 12, 17, 50) and a board (1), each shielded connector being connected to a predetermined side of said board (1) and being provided with at least one signal contact member (3) fitted in a hole (7) of the board (1), the connector having a shielded (61) to shield each signal contact member (3), wherein the board (1), except in area where connectors (2, 12, 17, 50) are fitted to the board (1), is provided with a first continuous electrically conductive layer (9) on one side and a second continuous electrically conductive layer (10) on the opposite side, each of the shielded connector housings being electrically connected to one of said layers (9, 10), in order to prevent electromagnetic radiation generated by any of said signal contact members (3) from propagating to the outside word.

The present invention relates to an assembly comprising at least oneconnector and a board, each connector being connected to a predeterminedside of said board and comprising at least one signal contact memberfitted in a hole of the board, the connector comprising electricallyconductive connector shielding means to shield each signal contactmember.

Such an assembly is known from U.S. Pat. No. 4,874,319, which isassigned to the Applicant of the present patent application anddescribes a connector-board connection to reduce the adverse effects ofelectromagnetic radiation generated by signal contact members extendingfrom the connector into the board. The known connector comprises aseries of leaf-type spring ground contacts positioned on opposite sidesof the signal contact members within the connector. A right-angleconnection is present between the connector and the board. To establishthis right-angle connection, the signal contact members and theleaf-type spring ground contacts each extend from the rear side of theconnector and are bend over 90°. However, the signal contact membersextend, unshielded, through corresponding through-holes in the board andare not entirely shielded. When very high frequencies, e.g. within thefrequency range from 50 MHz to 15 GHz, are used they still act asantennas radiating undesired electromagnetic radiation.

U.S. Pat. No. 4,697,858 discloses connections between a backplane andseveral printed circuit boards (pcb's) (FIG. 5). One side of thebackplane carries several chip elements each having several terminals.For example as shown in FIG. 7, some of those chip terminals areconnected to inner bus lines within the backplane through blind holesreaching as deep as the depth of the corresponding bus lines. Other chipterminals are connected to an inner ground plane through blind holesreaching as deep as the depth of that inner ground plane. Still othersignal carrying chip terminals are connected to signal pins extendingfrom the pcb's by means of signal contact members extending entirelythrough the backplane. These signal contact members extend fromconnectors accommodating the pcb's and being arranged at the side of thebackplane opposite the side carrying the chip elements. None of saidconnectors is shielded and the signal contact members extend unshieldedthrough said backplane. The bus line within the backplane is situatedbetween two separate ground planes in order to establish a well definedimpedance level. No EMC protective measures are provided for.

The present invention starts from the problem that in existing equipmentsignal contact members of a connector connected to a board, e.g. a pcbor a backplane, extend entirely through plated through-holes andgenerate electromagnetic radiation also at the opposite side of theboard. This will be explained referring to FIG. 1. FIG. 1 shows aconnection between a connector 42 and a board 41, e.g. a pcb or abackplane. One signal contact member 43 is schematically shown extendingfrom the connector 42 through a plated through-hole 40. It is to beunderstood that "signal contact member" is to be conceived as referringto those contact members of the connector 42 that are intended to carrysignals during operation, i.e. the not-ground members.

The connector 42 is provided with an electrically conductive layer 47 toshield contact member 43. Therefore, connector 42 is suited as coaxialconnector.

In existing connector-board connections each signal contact member 43extends from the through-hole 40 at the side of the board 41 oppositethe connector 42 or at least reaches the other side of the board 41, asshown in FIG. 16 of International Patent Application WO-NL-94/00075filed on Apr. 12, 1994, by the Applicant of the present patentapplication. Since the end part of the signal contact member 43extending from the board 41 is not shielded it acts like an antenna andradiates electromagnetic radiation which might induce cross-talk oraffect adjacent circuit elements.

The object of the present invention is to provide an assembly of a boardand at least one connector in which each signal contact member of eachconnector is prevented from radiating any undesired electromagneticradiation to the outside world.

To reach this object the assembly according to the invention ischaracterized in that said connector shielding means comprises ashielded connector housing enclosing each contact member, that each holeis provided with an electrically conductive layer on its inside surface,and that the board, except in areas where connectors are fitted to theboard, is provided with a first continuous electrically conductive layeron one side and a second continuous electrically conductive disposed inopposed relation to the first electrically conducting layer, each of theshielded connector housings being electrically connected to one of saidlayers, in order to prevent electromagnetic radiation generated by anyof said signal contact members from propagating to the outside world. Bythe application of these measures all shieldings of the individualconnectors and the electrically conductive layers on both sides of theboard provide a substantially leakproof shield against electromagneticradiation from the contact members. When the connectors have a coaxialor twinaxial function, such function is retained. By the application ofthe electrically conductive layer on the inside surface of each holecontact areas for connecting the signal contact members to other circuitelements, e.g. by means of a signal layer within the board, areprovided.

Preferably, the board comprises at least one electrically conductiveblind hole and at least one signal layer electrically connected to saidconductive blind hole, each signal contact member being fitted in acorresponding blind hole.

If required, one of said electrically conductive layers may be coveredwith an insulating layer, e.g. to protect said layer from engaging othermetal parts carrying a certain voltage.

In one embodiment of the assembly according to the invention a firstconnector is connected to one side of the board and a second connectoris connected to the opposite side of said board and one contact memberof the first connector is fitted in a first hole and one contact memberof the second connector is fitted in a second hole, the first and secondholes being aligned with each other. Since connectors may be connectedto the board opposite to each other and with aligned contact memberspackage density may be increased.

In such an embodiment, a ground layer may also be provided within theboard, separating the first and second holes.

Said first and second holes may be parts of one electrically conductivethrough-hole in such a way that said contact member of the firstconnector is electrically connected to said contact member of the secondconnector.

Each contact member may carry a signal in the frequency range of 50 MHzto 15 GHz. The assembly according to the invention provides excellentshielding against the antenna action of each contact member, even inthis range of frequencies.

Each blind hole may have a depth less than 1.5 mm and a diameter lessthan 1.2 mm. These dimensions may be obtained with current manufacturingmethods and allow for the application of blind holes in pcb's whichusually have a thickness of about 1.6 mm or more. Moreover, thesedimensions stimulate the progress of miniaturization in connectortechnology which is becoming more and more important but which demandsincreasing countermeasures against the adverse effects of the antennaaction of signal carrying contact members, especially in high frequencyapplications.

Preferably, each signal contact member is fitted to its correspondinghole by means of a press-fit connection. Such a connection offers greatmanufacturing advantages. However, alternatively, each signal contactmember may be fitted to its corresponding hole by means of a solderconnection. As a further alternative, contact members may be fitted intosockets inserted into the holes of the board.

The invention is also directed to a board of an assembly defined above,which board comprises at least said first electrically conductive layeron one side and said second electrically conductive layer disposed inopposed relation to the first electrically conducting layer, said layersbeing continuous except in areas where connectors are to be fitted,wherein holes for fitting contact members of said connectors areprovided in the board within said areas, each hole being provided withan electrically conductive layer on its inside surface.

Other object and further scope of applicability of the present inventionwill become apparent from the detailed description below, taking inconjunction with the accompanying drawings, in which similar parts aredesignated by identical reference numbers.

FIG. 1 is an assembly of a typical enhanced connector and a boardconnected together according to the prior art;

FIG. 2 is an assembly of a connector and a board connected togetheraccording to the present invention;

FIG. 3 shows an alternative assembly between some connectors and a boardaccording to the invention;

FIG. 4 is an enlarged cross sectional view of a blind hole in a boardaccording to the invention;

FIGS. 5a to 5d show enlarged views at level V--V in FIG. 4 of possiblecross sections of blind holes accommodating press-fit contact members,and

FIGS. 6 and 7 show cross sections of sockets which may be inserted inholes in a board according to the invention.

FIG. 2 shows an embodiment of a connection between a connector 2 and aboard 1 according to the invention. The connector 2 is provided with anelectrically conductive layer 61. The board 1 may be a printed circuitboard (pcb), a backplane or any other suitable substrate. Two signalcontact members 3 of the connector 2 extend from the connector 2 into aboard 1 in corresponding blind holes 7. To prevent any radiation fromthe signal contact members 3 to reach the outside world, the connector 2is shielded by appropriate shielding means. As known to a person skilledin the art, this shielding may be obtained by providing a plasticconnector coated with a conductive layer which is connected to ground.Alternatively, the connector 2 may comprise a separate metal housingenclosing all signal contact members. The shielding of connector 2 isconnected to a ground line or ground plane 9 arranged on the same sideof board 1 as the connector 2. The connection between the ground line orground plane 9 and the conductive layer 61 of connector 2 may beestablished by appropriate hold down means 8 which are known to personsskilled in the art.

Each of the blind holes 7 are plated with an appropriate metalliccoating. Said metallic coating contacts a signal layer 4 and/or 5. Byselecting a predetermined distance between the signal layer 4, 5 and theground plane 9 the impedance of said line 4, 5 can be predetermined,thereby providing the possibility of impedance matching to the connector2, as is known to persons skilled in the art.

The signal contact members 3 are fitted into the blind holes, e.g. by apress-fit method or by soldering. Each signal contact member 3 may beequipped with additional extensions to enhance electrical contactbetween each signal contact member and its corresponding blind hole.(This will be explained later by referring to FIG. 5).

A ground plane 10 is arranged on the side of the board 1 opposite to theconnector 2.

Since none of the signal contact members 3 extends from the side of theboard 1 opposite the connector 2 and that side is covered with theground plane 10 no disturbing radiation from the signal contact members3 can be radiated to the area below ground plane 10 (the term "below" ismeant to indicate the area at the side of the ground plane 10 oppositethe connector 2 and does not pose any limitation as to the scope of theinvention).

If required either ground 9 or ground plane 10 or both may be providedwith an insulating layer to prevent undesired short circuits to otherelectrical components or elements.

FIG. 3 shows a further embodiment of an assembly according to theinvention. In FIG. 3 the board 1 is connected to four shieldedconnectors 2, 12, 17, 50. Connector 17 has one signal contact member 11and is provided with an electrically conductive layer 62. Also connector12 has one signal contact member 13. It is to be understood that thenumber of signal contact embers shown either in FIG. 2 or FIG. 3 is notmeant in a limiting way. FIG. 3 shows that the signal contact member 11is fitted into a plated blind hole 37 which electrically contacts signallayer 4. Signal layer 4 also electrically contacts plated blind hole 27receiving one of the signal contact members 3 of connector 2.

Connectors 12 and 50 are connected to the side of board 1 opposite theconnectors 2, 17. Connector 12 is connected to the board 1 by the signalcontact member 13 which is fitted into a plated blind hole 28 whichelectrically contacts a signal line 16 within the board 1. Connector 12comprises an electrically conductive layer 63 which is connected to theground plane 10 by appropriate hold down means 29. To prevent radiationgenerated by the signal contact members 3 and 11 to reach the oppositeside of the board 1 a further ground plane 15 is arranged within theboard 1 separating blind hole 27 in the board 1 from the blind hole 28in the opposite side of board 1.

Blind holes in one side of the board may be non-aligned with blind holesin the opposite side of board 1. However, as shown in FIG. 3 some ofthem may be aligned. FIG. 3 shows that blind hole 27 into which one ofthe signal contact members 3 of connector 2 is fitted is aligned withblind hole 28 in the opposite side of board 1. To prevent cross talkbetween the signal contact member 3 fitted into blind hole 27 and signalcontact member 13 fitted into blind hole 28 further ground plane 15continuously extends between the end parts of signal contact member 3and signal contact member 13, respectively, as schematically depicted byreference number 14.

The board 1 with aligned blind holes 27 and 28 may be manufactured bythe following steps: forming a subassembly by pressing together underelevated temperature and pressure several board layers (for example 8),each 0.1 mm thick and each being appropriately provided with platedthrough-holes at predetermined locations--holes of all board layersbeing aligned at desired locations; pressing the electrically conductiveground plane 15 on said continuous substrate; pressing a further 0.1 mmthick substrate on said electrically conductive ground plane 15;pressing several further board layers (e.g. 8) each 0.1 mm thick andeach provided with plated through-holes at predeterminedlocations--holes of all board layers being aligned--on said furthersubstrate. Other manufacturing methods are possible. Conductive groundplane 15 may, for example, be an insulating, e.g. woven glass fibreresin material FR4, substrate coated with copper or any other metal.

Drilling blind holes in a board 1 is, in principle, also possible.However, the stacking method to produce the multilayer board 1, referredto above is more appropriate since after plating drilled blind holes, inpractice, often a conical shape of the plated blind hole having thesmallest diameter at the surface of the board will result. Thisaggravates the ease of insertion of a contact member into such a blindhole. Moreover, such a conical shape of plated blind holes may lead tobad electrical contacts between the plated blind holes and insertedcontact members.

FIG. 3 further shows the connector 50 provided with an electricallyconductive layer 64, which is connected to ground layer 10 withappropriate hold down means. Connector 50 comprises a contact member 51extending in a plated blind hole reaching as deep as the conductivelayer 5. Contact member 51 is, therefore, electrically connected toconductive layer 5. To prevent a short circuit to ground plane 15 thelatter is provided with a through-hole large enough to preventelectrical contact with contact member 51.

It is to be understood that it is also possible to provide one or moreplated through-holes through board 1 instead of blind holes whichthrough-holes receive one contact member of a shielded connector at oneside of the board and another contact member of another shieldedconnector at the other side of the board thereby establishing electricalcontact between both contact members.

FIG. 4 shows an enlarged view of a blind hole 7 in a board 1 into whicha signal contact member 3 is fitted. The blind hole 7 is plated with anelectrically conductive layer 44 which electrically contacts the signalline 4 within the board 1. To ease insertion of the signal contactmember 3 into the blind hole 7 the edge 39 of blind hole 7 to the sidesurface of board 1 is bevelled.

It is to be noted that in FIG. 4 the connector housing 2 and the groundplane 9 are left out for clarity only.

The maximum diameter d1 of blind hole 7 is, preferably, less than 1.5mm, whereas the diameter d2 of blind hole 7 within the board 1 ispreferably less than 1.2 mm and the depth h of blind hole 7 might beless than 1.5 mm. If the depth is smaller than 1.5 mm then two oppositealigned blind holes (like 27, 28 in FIG. 3) in a 3.2 mm thick pcb arepossible. Press-fitting in plated through-holes having a diameter ofabout 0.6 mm in a pcb having a thickness of 1.6 mm has already beenproposed in international patent application WO-NL-94/00075, filed Apr.12, 1994, mentioned above.

The cross section of a press-fit contact member may have differentshapes. FIGS. 5a to 5d show different appropriate shapes of press-fitcontact members 3 engaging the electrically conductive coating 44 of theblind hole 7. In FIG. 5d the signal contact member 3 is provided with anextension 6 which is arranged to establish a retention force between thesignal contact member 3 and the blind hole 7 when the signal contactmember 3 is fitted into the blind hole 7. Further details of such minipress-fit connections are described in international patent applicationWO-NL-94/00075, mentioned above, and all details as to these retentionmeans 6 are enclosed in the present patent application by reference.

It is to be understood that although all FIGS. 5a to 5d relate topress-fit connections, alternatively, solder connection means are alsopossible, e.g. the use of additional solder paste which after reflowestablishes a permanent soldered connection. However, press-fit ispreferred because of the additional ease of reparability. Moreover, theholes need not be plated.

Any other means to manufacture a conductive hole may be used, such as aconductive sleeve or an electrically conductive socket.

FIG. 6 schematically shows an enlarged cross-sectional view of aminiature insert socket 71 inserted in a blind hole 72. For furtherdetails of insert socket 71, reference is made to U.S. Pat. No.3,681,738 assigned to Berg Electronics, Inc. All details of insertsocket 71 disclosed by U.S. Pat. No. 3,681,738 are included in thepresent invention by reference. The insert socket 71 may be soldered inthe blind hole 72 by solder 73 which improves electrical contact tosignal layer 74.

FIG. 7 schematically shows an alternative socket 81 which may be used inthe present invention. The socket (or griplet) 81 is inserted into blindhole 82 and may, if desired, be connected to the side wall of blind hole82 by solder 83. By using solder 83 electrical contact between signallayer 84 and socket 81 is improved. Socket 81 is known as such from U.S.Pat. No. 3,504,328 assigned to Berg Electronics, Inc., the content ofwhich is included in the present invention by reference.

It may be clear to persons skilled in the art that FIGS. 6 and 7 showexamples of sockets and holes applicable in the present invention. Othersockets may be used. Moreover, through-holes may be applied instead ofblind holes and the application of sockets is not restricted to onesignal layer 74, 84 only.

I claim:
 1. An assembly comprising at least one connector (2) and aboard (1), said at least one connector (2) being connected to apredetermined side of said board (1) and comprising at least one signalcontact member (3) fitted in an electrically conductive blind hole (7)of the board (1) electrically connected to at least one signal layer (4,5), the connector comprising electrically conductive connector shieldingmeans (61) to shield at least one signal contact member (3)characterized in that said connector shielding means (61) comprises ashielded connector housing enclosing housing enclosing at least onecontact member (3), that each said hole (7) is provided with anelectrically conductive layer (44) on its inside surface and that theboard (1), except in areas where connectors (2, 12, 17, 50) are fittedto the board (1), is provided with a first continuous electricallyconductive layer (9) on one side and a second continuous electricallyconductive layer (10) disposed in opposed relation to the firstelectrically conducting layer (9), each of the shielded connectorhousings being electrically connected to one of said layers (9, 10), inorder to substantially prevent electromagnetic radiation generated byany of said signal contact members (3) from propagating to the outsideworld.
 2. Assembly according to claim 1 characterized in that one (10)of said electrically conductive layers is covered with an insulatinglayer.
 3. Assembly according to claim 1 characterized in that saidcontact member carries a signal in the frequency range of 50 MHz to 15GHz.
 4. Assembly according to claim 1 characterized in that the blindhole has a depth less than 1.5 mm and a diameter less than 1.2 mm. 5.Assembly according to claim 1 characterized in that each said signalcontact member is fitted to its corresponding hole by means of apress-fit connection.
 6. Assembly according to any of the claim 1characterized in that each said signal contact member is fitted to itscorresponding hole by means of a solder connection.
 7. Assemblyaccording to any of claim 1 characterized in that at least one hole (72,82) comprises a socket (71, 81) inserted into said hole.